[WWcvs] pg: HEAD -> rel-2-1-patches backport: "Fixed an error where any plane is

[Sam H. v. a. <act...@de...>]

Log Message:
-----------
HEAD -> rel-2-1-patches backport: "Fixed an error where any plane is
accepted if the d is 0 in ax + by + cz = 0." (dpvc)

Tags:
----
rel-2-1-patches

Modified Files:
--------------
    pg/macros:
        parserImplicitPlane.pl

Revision Data
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Index: parserImplicitPlane.pl
===================================================================
RCS file: /webwork/cvs/system/pg/macros/parserImplicitPlane.pl,v
retrieving revision 1.2
retrieving revision 1.2.2.1
diff -Lmacros/parserImplicitPlane.pl -Lmacros/parserImplicitPlane.pl -u -r1.2 -r1.2.2.1
--- macros/parserImplicitPlane.pl
+++ macros/parserImplicitPlane.pl
@@ -137,6 +137,11 @@
   if ($flag) {my $tmp = $l; $l = $r; $r = $tmp}
   my ($lN,$ld) = ($l->{N},$l->{d});
   my ($rN,$rd) = ($r->{N},$r->{d});
+  if ($rd == 0 || $ld == 0) {
+    return $rd <=> $ld unless $ld == $rd;
+    return $lN <=> $rN unless (areParallel $lN $rN);
+    return 0;
+  }
   return $rd*$lN <=> $ld*$rN;
 }